The development of next-generation flexible electronics, such as soft, portable electronic products, roll-up displays, wearable devices, requires flexible power sources. High capacity and fast charging speed are also very important for applications of high-performance flexible electronics. However, the fabrication of such an energy storage device remains a great challenge owing to the lack of reliable materials that combine superior electron and ion conductivity, robust mechanical flexibility, and excellent corrosion resistance in electrochemical environments.
Activated carbon (AC) is the most commonly used electrode material for supercapacitors and batteries due to their large surface area, porous structure for rapid mass transfer and ion diffusion, and low cost. However, AC suffers from low electronic conductivity (10-12 S cm−1) that can hinder the high rate performance of the AC electrode. Recent advances have demonstrated the potential of graphene and group IV-B elements (e.g., silicon, germanium, tin) for use in electrode applications such as secondary batteries and hydrogen storage of fuel cells. While graphene provides electrodes with high electrical conductivity, group IV-B elements, specifically Si-based systems, have been shown to provide electrodes with large theoretical specific capacity at room temperature (Li15Si4: 3600 mAh g-1) [1-3] and low operating voltage (near 0.1 V vs. Li/Li+). [1-3] Nonetheless, these materials still suffer from low specific capacity (LiC6: 372 mAh g-1), large volume changes during the cycling, and poor rate capability [1, 4].
Three-dimensional (3-D) foam is a very promising structure for providing better electrode materials for energy storage devices. One of the most important properties of 3-D foam is their high porosity (fraction of void volume to total volume) and high specific surface area, which has led to many applications concerned with gas storage, separations, and catalysis. Despite the potential of three-dimensional foam, the available methods for their synthesis are limited providing foams with large pore size and small surface areas. [5, 6].
Therefore, a need remains for electrode materials with greater surface area, high Li capacity, and high conductivity and improved methods for their synthesis.